Improvements in Information Technology and increased sophistication among data users have created extra demands for the Australian Bureau of Statistics (ABS). Data users require flexibility in how output is presented to them, for example, the flexibility to define their own geographic output areas, or to otherwise tailor output to their needs. The ABS is working to meet these needs, particularly with Population Census output where users are often interested in small areas or other small subpopulations. However, increasing the range of possible output introduces new challenges for the confidentiality protection of Population Census data. In particular, any system must protect against table differencing.
In this paper we describe the threat to confidentiality posed by table differencing, and review and comment on a number of techniques that could be used to develop a tabular confidentiality system that protects against differencing.